Ramadan, the monthlong ritual of fasting for Muslims world-wide, began for me this year on May 16. But no one at my New York mosque knew it would take place until the night before, when the crescent marking the beginning of the new month became visible above the horizon. Where skies were cloudy, mosques relied on the sighting of the crescent by mosques in sunnier places. Once a mosque certified the validity of the sighting, it would declare the official start of Ramadan. The Islamic calendar is based on the lunar cycle, and the beginning of a new month is subject to moon sighting.
Some...